The present invention relates to a turbocharger unit for a multicylinder internal combustion engine having at least two exhaust lines for the evacuation of exhaust gases from the combustion chamber of the engine and at least one inlet line for the supply of air to said combustion chamber, comprising at least one turbine which cooperates with at least one compressor to extract energy from the exhaust flow of the engine and pressurize the inlet air of the engine, which turbine is provided with a worm-shaped housing having at least two flow paths which are defined by means of tongues in the housing and which conduct mutually separate exhaust flows via stator blades to a turbine wheel.
The state of the art as regards turbocharger systems for the supercharging of diesel-type internal combustion engines, especially for heavy-duty vehicles, usually comprises a single-stage compressor driven by a single-stage turbine, both of the radial type.
Superchargers suitable for a diesel engine of 6 to 20 liter cubic capacity normally have an efficiency of between 50% and 60% (ηcompressor*ηmechanical*ηturbine) under stationary conditions. In contemporary diesel engines, the yield from good efficiency is lower than for future engines, which will require higher charging pressure. Examples of systems which increase the supercharging requirement are exhaust gas recirculation for lower-nitrogen oxide emissions or systems offering variable control of inlet valves. Turbocharger systems with higher efficiency than 60% under stationary conditions offer a greater prospect of meeting future requirements for environmentally friendly and fuel-efficient engines. To date, environmental demands upon diesel engines have usually resulted in poorer efficiency, which has therefore meant that the energy resource of the fuel has been less well utilized.
The turbine worm for a six-cylinder diesel engine is traditionally of the “twin-entry” type. The exhaust gases from cylinders 1-3 are conducted in one duct and the exhaust gases from cylinders 4-6 are conducted in another. These ducts run parallel right up to the turbine inlet, so that the division is made above the height of the blades. A turbine worm of the “double-entry” type may also be used. This type is made in such a way that the duct from one cylinder group provides 180° of the turbine inlet and the other cylinder group provides the remaining 180°. When the exhaust valves of the engine are opened, a powerful pulse of exhaust-gas is obtained. In a 6-cylinder engine, this pulse is generated alternately in the front and rear cylinder group at 120° (crankshaft) intervals. The pressures in the two groups may appear as in the diagram shown in FIG. 5.
Where a turbine worm of the “double-entry” type is used, together with inlet guide rails to the turbine, it is important that the ducts are kept separate for as long as possible; ideally they should not be joined until after the guide rails. The reason is that the pressure pulse from the one group (for example cylinders 1-3) must not leak over to the other, since it will be largely lost.
A conventional configuration of the guide rails can appear as shown in FIG. 3. The number of guide rails is expediently made as an even number, since two of the blades can lie directly adjacent to the two tongues of the worm. The worm-shaped turbine housing is normally produced with tongues, in one piece, by die casting. The guide rails are placed on an annular component which is fitted at the outlet opening of the turbine housing. For production reasons, therefore, the tongues cannot pass within the platform diameter of the guide rails.
It is desirable to produce a turbocharger unit which makes effective use of exhaust-gas pulses from a multicylinder engine in order to increase the transient response and efficiency of the engine.
A turbocharger unit, which is according to an aspect of the invention and which is configured for this purpose, for a multicylinder internal combustion engine having at least two exhaust lines for the evacuation of exhaust gases from the combustion chamber of the engine and at least one inlet line for the supply of air to said combustion chamber comprises at least one turbine, which cooperates with at least one compressor to extract energy from the exhaust flow of the engine and pressurize the inlet air of the engine, which turbine is provided with a worm-shaped housing having at least two flow paths which are defined by means of tongues in the housing and which conduct mutually separate exhaust flows via stator blades to a turbine wheel and is characterized in that each respective tongue meets a stator blade extended toward the tongue. This configuration of the turbocharger unit allows the efficiency to be kept high, at the same time as transient response is improved.